Ice2ice researcher Christian Rodehacke is co-author on a new article in The cryosphere investigating different models of Greenland ice sheet and how they compare.

We have compared a wide spectrum of different initialisation techniques used in the ice sheet modelling community to define the modelled present-day Greenland ice sheet state as a starting point for physically based future-sea-level-change projections. Compared to earlier community-wide comparisons, we find better agreement across different models, which implies overall improvement of our understanding of what is needed to produce such initial states.

Common ice mask of the ensemble of models in the in-tercomparison. The colour code indicates the number of models(out of 35 in total) that simulate ice at a given location. Outlinesof the observed ice sheet proper (Rastner et al., 2012) and all ice-covered regions (i.e. main ice sheet plus small ice caps and glaciers;Morlighem et al., 2014) are given as black and grey contour lines,respectively.

Again this year ice2ice is very will be very well represented at European Geophysical Union meeting running from 8-14th of April in Vienna. Below some of the sessions, presentations and posters that will be presented or is co-authored by ice2ice. But please do keep updated at https://www.egu2018.eu/

EGU2018-5122Fault activity and diapirism in the Mississippian to Late Cretaceous Sverdrup Basin: New insights into the tectonic evolution of the Canadian Arctic by Berta Lopez Mir, Peter Hulse, and Simon Schneider

EGU2018-10339On scale break in the climate spectrum at glacial time scales by Peter Ditlevsen, Michel Crucifix, and Takahito Mitsu

08:45–09:00

EGU2018-18392At which spatiotemporal scales, and in which climate states, can the linear temperature response hypothesis be rejected by data? by Hege-Beate Fredriksen, Martin Rypdal, and Kristoffer Rypdal

EGU2018-6808Linking Greenland to the Pacific northwest with the Khangar Tephra. First identification of cryptotephra from the Kamchatka Peninsula in a Greenland ice core. by Eliza Cook, Maxim Portnyagin, Vera Ponomareva, Lilia Bazanova, Anders Svensson, and Dieter Garbe-Schönberg

“But is that significant?” You have probably heard that question many times. Perhaps you can confidently say “Yes it is”. Perhaps you don’t know. Perhaps you are not enitrely sure how to test if it is significant or not. Perhaps you just used a build-in tool in your favourite program, got a p-value that looks reasonably and say “sure, that looks significant enough”. Regardless of you being a statistical master or apprentice, you just missed out on a great opportunity to learn even more statistics.

by ice2ice PhD Ida Ringaard

To brighten up cold and weary February in Copenhagen, Ice2ice hosted a climate statistics workshop. Over three days, the three instructors Martin Miles (UniResearch), Francesco Muschitiello (University of Cambridge) and Peter Thejll (Danish Meterological Institute) guided the 12 participants (6 PhD students, 3 masters students, 2 senior researchers and 1 postdoc) through the jungle of statistics.

First things first, you have to be able to crawl before you can walk. Therefore, Martin spend the first day making sure everyone could crawl i.e. getting everyone up to speed with the basic descriptive and inferential statistics (looking at the distribution of the data, computing probabilities and confidence levels). Having mastered the theory, it was now time for the practical part. Francecso steered us through practical hands-on exercises of what we just learned using the statistical program R.

Next day was all about correlation, regression and handling errors. Martin started the day by going through correlation theory and potential pitfalls, as well as the basics of regression analysis. Peter followed with more advanced regression analysis, which assumptions are made, how to handle errors in x or y-direction, or the combination of both etc. After a well deserved (and needed) lunch break, Francesco ended the day by lecturing about Monte Carlo simulations, live-coding examples on how to do it in-practical at the same time.

The last day with planned lectures started off with Martin talking about time- and time-frequency analysis. Francesco was once again in charge of transforming the theory into practical use. After spending 2.5 days on learning time series analysis, the afternoon lecture lead by Martin switched gear and briefly touced upon spatial analysis, spatial autocorrelation and regression and EOF’s.

Too not end this statistics workshop too abruptly, there was no official program on Friday. Instead, Martin hung around, ready to help the participants with questions regarding their own data.

This rounded up a very rewarding, intense and actually fun statistics workshop, worth repeating. For me at least, is was very helpful to see the theory used on time series and data that I actually use in my research and can relate to.

Markus, Roman and I recently published a paper in Ocean Modelling (which can be found here: https://doi.org/10.1016/j.ocemod.2018.01.008) about the representation of the Southern Ocean in climate models. Here is a short summary of our study as well as our take on how this piece fits into the ice2ice puzzle.

The schematic shown in Figure 1 places the Southern Ocean at the center stage in the modern view of the large-scale ocean circulation. Not only does it allow for an exchange of properties between the three major ocean basins via the Antarctic Circumpolar Current (ACC), it is also a key region of wind-driven upwelling due to persistent overlying westerlies and hence provides closure for the meridional overturning circulation. From a present-day perspective, these properties of the Southern Ocean are important to oceanic uptake of anthropogenic heat and carbon dioxide, as well as the oceanic poleward heat transport.

FIG1: Schematic from Talley (2013)

The issue with the representation of the Southern Ocean in ocean general circulation models (OGCMs) is that mesoscale eddies (Figure 2), a vital component to the dynamical balance that prevails in the Southern Ocean, evolve on a spatial length scale which is smaller than the typical ‘coarse’ horizontal grid resolution in commonly-used climate models (about 1 deg. X 1 deg.). That is, the effect of eddies on the large-scale ocean circulation is not present unless we parameterize it in the model. This problem has a long history in the oceanographic literature, and how to parameterize the effects in practice is still hotly debated. The vastness and remoteness of the Southern Ocean means that we do not have a reliable observational constraint on what it is that we attempt to parameterize, but a considerable amount of theoretical and modelling studies have given us a reasonable idea about what properties such parameterization needs to fulfill.

In our study we decided to compare a commonly used climate model, with an implemented eddy parameterization, to a high-resolution version of the same model, with explicitly resolved eddies, to examine how well the coarse resolution model mimics the physics. A forward integration of a global eddy-resolving OGCM is a demanding computational task why this study was only made possible through granted computer time at the supercomputer in Jülich, Germany, and support from the NBI e-science section. Using 4096 cores of the IBM BlueGene, the experiments generated about one Petabyte model output, required a continuous data transfer of about one Terabyte pr. day and took three years to complete.

Perhaps the most important eddy effect in the Southern Ocean is that eddies drive an overturning circulation of opposite sign to the one set by the winds alone i.e. it compensates the wind-driven upwelling of water. To keep it short, we found that the coarse resolution model distributes the eddy-circulation differently across water masses compared to the high-resolution model, which imply that the eddy compensation is different between the models (Figure 3). We also found that the total southward heat transport in the Southern Ocean compares well between the models, but that the heat transported by the eddy field alone is different. These two results indicate that there is room for improvement in the formulated eddy parameterization.

Fig3: Southern Ocean overturning streamfunctions in latitude-density space. The left and right column of panels is from the coarse and high resolution model, respectively. The upper panels show the total flow, the middle panels the mean-flow and the lower row the eddy-induced circulation. The sum of the mean-flow and the eddy-induced circulation equals the total flow. Units are in Sverdrups (1 Sverdrup = 1 million m3 / s). Adopted from Poulsen, Mads B., Markus Jochum, and Roman Nuterman. “Parameterized and resolved Southern Ocean eddy compensation.” Ocean Modelling (2018).

This is all fine, you may say, but why is this relevant to the ice2ice community? A satisfactory theory for global-scale abrupt climate change, such as D-O events, has to explain how the northern and southern hemisphere exchange information in order to arrive at the d18O signals that we find in the ice cores from Greenland and Antarctica. If the information of climate change between the hemispheres is transmitted through the ocean, the climate signal has to cross the ACC. Here models often struggle, which either tell us that the signal does not transmit through the ocean or that it does but the relevant physical processes are not well represented in the models. A substantial amount of heat is fluxed poleward across the ACC by mesoscale eddies, which our study indicates is distributed wrongly in the coarse resolution model. If eddies do play a role in transmitting the climate signal, a better mesoscale eddy parameterization might be needed to obtain the correct response in OGCMs.

The annual all staff meeting was held in Sweden in start of February. 55 internal ice2ice researchers attended the meeting and had intense focus on synergies within ice2ice.

The annual all ice2ice staff meeting was held in Mölle, Sweden.

The scope for this year’s all-staff meeting was synergies in Ice2ice. We are at the state in the ice2ice project where several great publications has allrady been publishedfrom the individual ice2ice researchers, expanding the knowledge on how sea ice and land ice influence each other (the full list of ice2ice publications so far can be seen here). However to fully benefit from the versatile group of people we are within ice2ice this years all staff meeting was set up with a focus on collaboration and synergy between the individual institutions.

ice2ice PI Bo Vinther kicking off the 1 min/1 slide presentations with an update on water isotopes in ice cores and what they can teach us about past temperature and accumulation.

To get everyone up to date on the new and exiting research that has happened within ice2ice since last year, each staff member quickly introduced their science with a 1 minute slide. Further a poster session was used to update on ongoing research.

Happy ice2ice researchers during the poster session

The remaining workshop was used to identify and start the process of writing synergy papers. We split into 6 working groups, each with a theme covering part of the overall work packages of ice2ice:

Each working group discussion was initiated by a few scientific talks and from there continued discussions over two days led to the concrete identification of at least 2 synergy paper per group. In several groups more than 2 ideas for ice2ice synergy papers came out of the fruitful discussions. Making for a busy, but exciting period until the end of the ice2ice project by September 2019.

Also time for a few walks and talks during the meeting.

Such a close collaboration on papers can only be facilitated when researchers know each other well, thus we also found time for social excursion to Kullaberg led by a geologic expert.

Eva presenting a word cloud of the feelings of high school children about climate change

The Folgefonn Centre in Rosendal, a two hour boat ride South East of Bergen, was the base of nine ice2ice PhD students from Bergen and Copenhagen for four days in late January. They set out to engage in a dialogue with different audiences to improve their science communication skills. The PhD students formed groups of two to three and aimed to find out what 12 to 13 year-old children from Omvikdalen barneskule and 16-year old teenagers from Kvinnherad vidaregåande skule want to learn about the local and global climate. A third group met tour guides and representatives of the local turistforening.

On Monday the groups visited their individual audiences. Kartia and Sunniva, the elementary school group, asked the children what they would like to know about climate change and asked them to draw pictures regarding climate. Many of the children drew the local Folgefonna glacier and sea ice and were very interested in sea level rise. The children got a sneak peek into the daily life of a climate scientist by working with a microscope and running a simple climate model.

Anaïs, Eva, and Ida, the high school group, chose a different approach. The teenagers were asked to write down words that came to their mind when they think about local climate, global climate and climate change.

Silje and Jonathan presented the idea behind the “Turspor”-project to tour guides and the local turistforening. “Turspor” is an outreach project of the University of Bergen that provides descriptions of local landscapes and their development for hiking trails. But getting to know their audience was only the first step.

The PhD students were going to meet their audiences again the following Thursday. So they had two days to work out how they would answer the questions of their audiences. Thursday was a busy day at the Folgefonn Centre.

Sunniva explaining the card game and Mathew assisting with the sediment core.

First the high school children came. Anaïs, Eva, and Ida started with the whole group and presented word clouds of what the teenagers wrote down on Monday. Then the three PhD students discussed different aspects of their common theme “ice melting” in individual groups. Anaïs explained stratification of the ocean and illustrated it with an experiment. Eva talked about how she is reconstructing past climate changes with the help of marine sediment cores. And Ida focused on the change of Arctic sea ice from a modeling perspective and how it might influence the local climate.

The elementary school children came to the Centre shortly after. Karita and Sunniva answered the children’s questions in a card game where the children had to match their questions and Karita’s and Sunniva’s answers. The children got excited about investigating a sediment core from the Arctic Ocean and seeing an experiment illustrating the difference between melting sea and land ice.

In the afternoon, Silje and Jonathan presented their interpretation of the development of local landforms and how they plan to write up a “Turspor” as an addition for a local hike trail project in Rosendal.

In the end everybody was happy, audiences and PhD students alike. It was a great week where all of us learned a lot. We thank everybody involved for their efforts, and especially Mathew Stiller-Reeve for his enthusiasm and support in the planning phase and during the bootcamp week. He also gave a great lecture with tips on writing skills. Furthermore, we want to thank Ellen Viste for her very nice lecture on presentation techniques. But the whole week would not have been possible without the dedicated teachers at the local schools and especially the employees of the Folgefonn Centre, Karen Løvfall Våge and Ivar Baste. Science communication works best when you initiate a dialogue with your audience to make sure that you really address relevant topics. Go out and talk to your audience :-)!

Henning Åkesson successfully defended his thesis ”Deglaciation of the Norwegian fjords” 9th of January 2018 at the University of Bergen. Henning is closely affiliated to the ice2ice project and has combined ice flow models with geological and paleoclimatic data to study the dynamics and response to climate of marine outlet glaciers and ice caps in western Norway and Greenland. Henning’s supervisors have been Kerim H. Nisancioglu, John Inge Svendsen (UiB) and Mathieu Morlighem (Univ. California, Irvine), and his thesis consists of five papers; one already published, three in review and one to be submitted.

The new doctor has already got a new job. He will continue his academic career as a postdoc at Stockholm University, modelling Greenland outlet glaciers of the past.

The main scope of the thesis was to study the behaviour of the western Scandinavian Ice Sheet during the last deglaciation. Henning also co-authored a paper on changes to Jakobshavn Isbræ since the Little Ice Age, West Greenland, as well as lead a paper on Holocene evolution of an ice cap in southern Norway.

In his first paper, Henning and co-authors studies dynamics and sensitivity to climate change of the Hardangerjøkulen ice capin southern Norway. They use the numerical ice flow model ISSM constrained by glacier and climate reconstructions to simulate ice cap evolution since the mid-Holocene. Here, they find that Hardangerjøkulen grows non-linearly since ice cap inception and that present-day Hardangerjøkulen is exceptionally sensitive to climate change. The latter is related to a flat surface topography and an associated effective surface mass balance-elevation feedback. Read the full paper here.

The second paper shows that fjord width strongly controls the stability of marine-terminating glaciers. Henning and co-authors use an ice flow model purpose-built for fast-flowing outlet glaciers on a suite of idealised fjord geometries, representative of real-world glaciers. They show that identical warming ocean conditions may cause grounding line retreat varying by several tens of kilometers depending on the fjord geometry. The paper is in review.

The third paper gives a decadal to centennial scale perspective of the abrupt retreat of Hardangerfjorden glacier in western Norway at the Younger Dryas–Holocene transition. This well-dated paleoglacier is an excellent past analogue of Jakobshavn Isbræ in Greenland (Paper 4), and other similar outlet glaciers in Greenland, Alaska, and Patagonia. Using the ice flow model from Paper 2 they find that high surface melt and warmer fjord waters are likely triggers and drivers of the reconstructed fast retreat. The study suggests a highly variable retreat history paced by fjord bathymetry and ice tongue buttressing. Periods of high retreat rates contribute significantly to the overall length of retreat, yet these rates are not sustainable for more than a few decades. The paper is to be submitted.

The fourth paper studies the fastest flowing glacier in the world; Jakobshavn Isbræ in western Greenland. This glacier’s floating tongue suddenly collapsed in the early 2000s, with a fast retreat and tripling in speed occurring since. Nonetheless, it is unclear to what extent Jakobshavn’s past history influences its modern retreat. Henning is a co-author on this study, which simulates the history of Jakobshavn since its Little Ice Age (LIA) maximum position in year 1850. The authors find that the glacier responds non-linearly to a linear strengthening in external forcing. The changing forcing following the LIA triggers retreat, while fjord geometry controls the variability of the modelled non-linear retreat history. Because of intermittent grounding line stillstands at geometric pinning points, retreat may be delayed by several decades, only to be followed by an abrupt grounding line migration without additional forcing.

In the fifth paper, Henning and co-authors use the ice flow model ISSM to study deglaciation of the fjords at the Norwegian west coast. Using a first-order climatology based on paleo-records, they suggest that a warming ocean is a highly potent trigger for swift decadal scale grounding line retreat. However, the study finds that multi-millennial deglaciation in this region was driven by surface melt. In addition, the authors find that topography heavily controls the sensitivity marine ice sheet margins; glaciers in fjords with bottleneck inlets and/or shallow sills were significantly more resilient to ocean warming, while wide and deep troughs allow for extensive retreat.

Combined, Henning’s thesis shows that the topography of the landscape itself is fundamental to the sensitivity of glaciers terminating in fjords. His results also suggest that ocean warming and grounding line dynamics are important controls of marine-based retreat over time scales up to a century or two. Beyond these time scales, the atmosphere is found to be the most important driver of ice sheet mass loss.

Article in Bergens Tidende 10th January 2018

Henning’s findings on the retreating Norwegian glaciers and likely disappearance within this century, if carbon emissions are left unabated, caught the attention of several broadcasters.

The local newspaper Bergens Tidende had a one pager where they present and discuss his work and the consequences for people and society. You can read the article here.

NRK produced this article about the possible dissapreance of the Hardangerjøkelen glacier within a few decades.

Henning also talked about the demise of Norwegian glaciers as a guest in studio at the news channel TV2 Nyhetskanalen. This was broadcasted live on Saturday 13th of January 2018.

Our two most recent ice2ice Phds; Sunniva and Karita Kajanto, are already busy spreading their knowledge. They have engaged with Norwegian school children to help them understand how the Arctic is currently changing due to sea ice disappearing and the consequences on climate.

Christmas holidays and the turn of the year are soon over us. With snow for those who are eager to explore the seasonal cryosphere, and family gatherings and relaxation in line for most of us. 2017 has been an exciting year for our project, where we have taken decisive steps to start integrating results and we start to see how all of our efforts come together. Papers and PhD theses are being produced in increasing numbers and many of you are now active in cross-team integration efforts which we hope will be central in the upcoming all staff in a month or so.

The PIs have started to work on the integration with input and results from many aspects of the project, and we have on the horizon a series of new discoveries we believe have the potential for providing the breakthroughs we promised in our proposal. It is a great privilege to be part of ice2ice which have so many talented and devoted participants, not least the fantastic atmosphere and enthusiasm we experience in the project on all aspects of science, training, mentoring and outreach.

We are very much looking forward to working closely with all of you on exiting science in the coming year, and with this wishing you all a merryChristmas and a Happy New Year!

Mari F jensen successfully defended her PhD thesis 1st of december -2017 on “Abrupt changes in sea ice and dynamics of Dansgaard-Oeschger events”. Mari is the second ice2ice Phd to finish her studies. Luckily Mari has decided to continue in Science, a great benefit to all of us and the ice2ice objectives. Through her Phd Mari has published 1 peer reviewed article and submitted another two, that all form part of her thesis. You can read and download the thesis here.

Mari F Jensen and supervisor Kerim Nisancioglu after the defense.

The subject of Maris thesis has been to study the dynamics of Dansgaard Oeschger events. Changes in sea ice are proposed as an important component in Dansgaard-Oeschger events; the abrupt climate change events that occurred repeatedly during the last ice age. Paleoclimatic reconstructions suggest an expansion of sea ice in the Nordic Seas during the cold stadial periods of the Dansgaard-Oeschger cycles. However, as the present configuration of the Nordic Seas does not allow for an extensive sea-ice cover in this region, the hydrography must have been different during glacial times. In fact, reconstructions show that the Nordic Seas hydrography during cold stadial periods was similar to the stratification of the Arctic Ocean today. However, the dynamic impacts of changing freshwater input and Atlantic water temperature on the Arctic stratification and sea ice are unclear.

Maris study aimed to assess the potential for Arctic-like stratification in the Nordic Seas during the last glacial period and the dynamics behind Dansgaard-Oeschger events, using models and theory. The results are presented in three papers.

In the first paper, she and co-authors developed a simple conceptual two-layer ocean model including sea ice representing the Nordic Seas during stadial times. Here, they find that the sea-ice cover is sensitive to changes in freshwater input, subsurface temperature, and the representation of vertical mixing. Abrupt changes in sea ice can occur with small changes to surface freshwater supply or Atlantic water temperatures. You can read the full paper here.

In the second paper we apply a three-dimensional eddy resolving numerical model to the same problem and find further support for the conclusions from the first paper; the stability of a sea-ice cover in the Nordic Seas is dependent on the background climate and large changes in stratification and sea ice occur with small changes in forcing. In addition, additional results presented in this dissertation show self-sustained oscillations in sea-ice cover without a change in forcing. From the second paper, it was shown that an extensive sea-ice cover and an Arctic-like stratification with a fresh surface layer and a halocline can exist in the Nordic Seas without an external freshwater supply. Under sufficient cold conditions, a halocline capped by sea ice emerges spontaneously due to redistribution of freshwater through sea-ice formation and melt. Further it was shown that an extensive sea-ice cover slows down the local overturning in the Nordic Seas; decreases the heat import to the basin; warms intermediate waters, and cools deep waters. The paper is under review.

In the third paper, the importance of background climate is further stressed. In this study, rather than studying an Arctic-like stratification, the focus is on sea-surface temperature variability in the region of the Nordic Seas and North Atlantic. Mari and co-authors compile all available planktic foraminifera records from the North Atlantic during Dansgaard-Oeschger events with a sea-surface temperature reconstruction. These are then combined with fully coupled climate model simulations using a proxy surrogate reconstruction method. The resulting spatial sea-surface temperature patterns agree over a number of different general circulation models and simulations. However, freshwater forced runs from glacial times are needed to capture the amplitude of the temperature variability as seen in the proxy records. They suggest that sea-ice changes are important in extending the oceanic temperature signals to land. You can read the submitted paper here.

Combined, the three papers argue for an important role of the Nordic Seas during DansgaardOeschger events, consistent with paleoclimatic reconstructions. Maris results are also relevant for understanding potential future changes in Arctic sea-ice cover, and we argue that changes in Atlantic water temperature are of large importance.